This application proposes a continuation of studies examining the handling of self proteins by antigen presenting cells (APC). These studies are geared to examine the issue of central tolerance from the perspective of the processing and presentation of self molecules. During the past two years, Dr. Allen and coworkers have developed a model to study the processing and presentation of the self protein hemoglobin (Hb). Using this system they obtained direct proof that self hemoglobin/Ia complexes are expressed constitutively in vivo. This demonstration of the inability of Ia molecules to distinguish between foreign and self antigens has tremendous implications for the processes of self tolerance and autoimmunity. These workers now propose to continue studies using the hemoglobin system as well as develop other new antigen systems. Initially they will examine non-lymphoid organ APC for the expression of the Hb/Ia complexes. The investigators will then examine all of the different cell types, both lymphoid and non-lymphoid, shown to express the Hb/Ia complexes for their ability to express co-stimulator molecules which are required for T cell activation. It is then proposed to develop three new antigen systems with which the processing and potential presentation of other self proteins will be examined. These antigens are: 1) a sperm-specific heat shock protein, HSP70.1, which is developmentally expressed during puberty; 2) glial fibrillary acid protein, a protein only expressed in astrocytes in the brain and is thus compartmentalized; and 3) B-galactosidase, a protein which is contained in lysosomes and circulates in low levels. By studying these three different antigen systems the investigators will be able to further understand how the immune system copes with various self proteins. It is also proposed to ascertain the molecular basis of the non-responsiveness of B10.BR mice to the peptide determinant Hbb(67-76) which is due to a non-gene. This non-responsiveness could be due to a deletion of a particular VB as has been observed for Mls, or a self protein which has a cross reactive determinant, and the process of self tolerance to this protein eliminates the reactive T cells to Hbb(67-76). Finally, it is proposed to generate monoclonal antibodies against peptide antigens which will recognize these antigens only when they are bound to an Ia molecule. From these proposed studies one could gain a better understanding of the handling of self proteins by antigen presenting cells, the results of which may aid in the design of better vaccines and the prevention of autoimmune diseases.